(a) Field of the Invention
This invention relates to diaphragms to be used for electro-acoustic transducers such as loudspeakers and the like and a method of making the same.
(b) Description of the Prior Art
There are already known diaphragms for loudspeakers using ceramics material high in the heat stability and Young's modulus. In a conventional ceramics diaphragm, there is a problem of reducing the weight of the diaphragm. Therefore, in order to reduce the diaphragm weight, void spaces are formed in a ceramic plate to reduce the apparent specific gravity. For example, in Japanese Patent Preliminary Publication No. Sho 56-69995, a honeycomb structure made of ceramics is disclosed. However, ceramics are so brittle that it is very difficult to form a honeycomb structure of ceramics and it has been practically impossible in case the manufacturing cost is considered. Generally, as shown in FIGS. 1a to 1c, the honeycomb structure is made by piling up flat plate members 2 with a bonding agent 1 zigzagging among them (FIG. 1a), pressing the members 2 into contact with one another (FIG. 1b) and expanding them (FIG. 1c). However, in the thus-made honeycomb structure, the bending stiffness in the direction at right angles with the expanding direction will be about twice as high as the bending stiffness in the expanding direction and the bending stiffnesses in both of these directions will vary also depending on the expanding degree (fluctuation of the pulling force). Therefore, the vibration mode will not be axially symmetrical. For example, in a circular flat plate diaphragm, the node shape appearing on the diaphragm surface (the line connecting the positions in which the amplitude is zero on the diaphragm) will be elliptical and a magnetic circuit having an elliptical voice coil and elliptical magnetic gap will be required to make a node drive (driving in the node position) and will be very difficult to produce.